The present invention relates to composite pipe assembly, for example a composite pipe assembly for use in oilfield applications, and to a method of preparing the same. The present invention further relates to a method of a repairing a composite pipe and to the repaired pipe so produced.
Composite materials are finding increasing application in the replacement of metal. One field in which the use of composite materials is receiving increasing attention is in the manufacture of pipes and pipelines, in particular for use in oilfield exploration, drilling and production operations. Examples of applications for composite pipes are composite risers, including both composite drilling risers and composite production risers. Other applications include mooring tendons for offshore platforms, as well as choke lines, kill lines and auxiliary lines. Specification 17J of the American Petroleum Institute defines the specifications for unbonded flexible pipe.
The construction of composite pipes may take a variety of forms, depending upon the intended application of the pipe. Generally, composite pipes comprise a plurality of layers of material, the selection of the layers being determined by the intended application. U.S. Pat. Nos. 5,261,462 and 5,435,867 disclose a tubular structure, for example a pipe or a pressure vessel, comprising a wall formed from plastic, composites and elastomeric materials. The composite materials are wound in a spiral manner, separated by strips of elastomer. A mandrel is typically employed, over which the layers of material are wound or applied, after which the mandrel is removed.
As with all piping, composite pipes require end fittings to be provided in order to allow lengths of pipe to be coupled together or to allow the pipe to be connected to other pipes or apparatus. However, unlike conventional pipes, such as those made of steel, it is not possible to fashion couplings and end connections of the composite materials very easily or to connect standard metal fittings to the ends of composite pipe runs. In oilfield applications, as in many industries, it is very common to employ standard fittings, such as flanges and other couplings, with standard dimensions and thread patterns or other fastener arrangements. Accordingly, it would be highly desirable to provide a means of connecting such standard fittings to composite pipes.
A number of approaches have been taken to this problem. One approach is described by W. F. Andersen in xe2x80x9cAdvanced Composite Drilling Risersxe2x80x94Providing Cost Effective Systems for Deepwater Exploration and Productionxe2x80x9d, Deepwater Technology Symposium, Dec. 2-5, 1997. Andersen describes the use of a so-called xe2x80x9cgeometric trapxe2x80x9d, in which a standard end connector is attached to a metal insert. The metal insert is wound into place during the fabrication of the composite pipe using a mandrel. A dome on the metal insert prevents the insert from being pulled out of the end of the composite pipe when in use. Once the fabrication has been completed, the mandrel is removed and the ends of the composite pipe machined to reveal the metal insert. A fitting or connector is then welded to the exposed end of the metal insert. Andersen notes that a special technique is required in order to cool the metal insert during the welding process, in order to avoid damage to the composite material of the pipe due to exposure to the heat generated by the welding process. Clearly, the need for such a welding step or the precautions required in order to prevent damage to the composite material is undesirable.
U.S. Pat. No. 4,701,231 discloses a method of forming a joint between a tubular composite and a metal ring, in which the metal ring is provided with a surface of given geometry, over which the composite material is wound during the fabrication of the tube. The geometry of the surface of the ring is determined so as to form an interference fit between the composite layers and the ring. In a development of this form of fitting, U.S. Pat. No. 5,771,975 describes a composite marine riser, in which an end connection is present having a segment over which the composite material is applied. Again, the segment of the end connection is provided with a contoured surface so as to prevent the withdrawal of the segment from the end of the riser. In a preferred embodiment, the end connection comprises two such segments over which the composite material is wound. Thereafter, the two segments are forced apart in order to provide an axial pre-load on the composite material.
It will be clear that the aforementioned approaches to the provision of end fittings in composite pipes all require the end fitting to be present and built into the pipe during the fabrication process. It would be desirable to provide end fittings and a method of applying them which could be applied to completed sections of composite pipes as and when required. Further, the forms of joint disclosed in U.S. Pat. Nos. 4,701,231 and 5,771,975 have a joint capacity that is dependent upon the strength of the composite material in the radial and circumferential directions of the pipe. This can be very limiting on the capacity of the joint to withstand high axial loads.
U.S. Pat. Nos. 5,261,462 and 5,435,867 disclose a method by which lengths of the composite pipe describe therein may be joined. In this method, various layers of the end portion of each length of pipe to be joined are cut away, revealing the innermost layer or liner. The lengths of pipe are joined by welding the ends of the liners together, after which composite material is wound around the joint. The joint is completed by the application of a plastic sleeve. U.S. Pat. Nos. 5,261,462 and 5,435,867 suggest, as an alternative, the use of a coupling having helical recesses over which the composite layers could be wound. It will be appreciated that this operation is both time consuming and costly in terms of the additional materials needed in order to fabricate the joint. In addition, the resulting joint is limited in its load capacity and efficiency.
U.S. Pat. No. 5,443,099 discloses a tube of a composite material having a metallic end coupling connected to one end. The end coupling is provided with an inner member, which extends within the end portion of the tube, and an outer member, extending along the outside of the end portion. Metallic pins extend through the outer member and the composite material into the inner member in order to secure the end coupling in place and prevent its withdrawal from the end of the tube. While such an arrangement can be applied to a completed composite pipe, the reliance upon metallic pins can compromise the integrity of the composite layer, causing points of stress concentration and leading to eventual failure.
U.S. Pat. No. 5,895,079 discloses a threaded connector for joining two lengths of composite pipe. The connector comprises a single, double ended tapered male member which extends into the end portions of the two pipes being joined. The outer tapered surface of the connector is formed with a thread to match corresponding threads on the inner surfaces of the end portions of the pipes. The connector may be applied to form a joint between two lengths of completed composite pipe. However, its application relies upon a thread being machined into the end portions of the pipes being joined. Such a machining operation is undesirable, particularly when use of the connector in remote oilfield locations is envisaged.
U.S. Pat. No. 5,685,576 discloses a pipe coupling for application to a completed composite pipe. The coupling comprises a male conical member to be inserted between the inner layers and outer layers of the end portion of the composite pipe. A female conical member or cup is placed over the end portion of the composite pipe. A filler is applied to fill the voids between the male and the female conical members. An axial force is applied between the male and female members in order to clamp the composite layers between the conical surfaces of the two members. Again, while this form of connector may be applied to a completed composite pipe, it requires a substantial operation to separate the layers of the composite pipe in the region of its end and to install the male and female members. The need for such an operation and the reliance of the joint on filler materials renders this form of joint a disadvantage when use in remote locations is envisaged.
Accordingly, it will be appreciated that there remains a need for a connector or end fitting for a composite pipe which may be applied to a finished pipe, as required, without the need for extensive machining or other operations.
According to a first aspect of the present invention, there is provided a composite pipe assembly comprising a pipe having a pipe wall with an inner surface and an outer surface; a housing comprising a tubular portion having an inner surface, said tubular portion disposed around the outside of the pipe; and a tubular forge member having an outer surface, said forge member disposed within the housing whereby a portion of the pipe wall is disposed between the inner surface of the tubular portion of said housing and the outer surface of said forge member; the forge member having been deformed radially outwards against the pipe and the housing and the tubular portion of the housing having been deformed radially outwards to a partial yield point; the tubular portion of the housing applying a compressive force radially inwards against the pipe wall and the forge member. The forge member preferably applies a force radially outwards against the inner surface of the pipe wall. The forge member is preferably deformed to beyond its yield point.
In applications in which the composite pipe assembly is to be subjected to high axial loads, for example in drilling risers and production risers for offshore oilfield operations, it is preferred to provide one of the inner surface of the tubular portion of the housing and the outer surface of the forge member with at least one rib. More preferably, both the inner surface of the tubular portion of the housing and the outer surface of the forge member are provided with a rib, the ribs being offset from each other in the axial direction of the pipe. For some applications it is most advantageous to provide a plurality of ribs and grooves on the inner surface of the tubular portion of the housing and the outer surface of the forge member, each rib being axially aligned with an opposing groove. The ribs, if provided, are preferably shaped so as not to penetrate or puncture the surface of the composite pipe. The ribs, if provided preferably extend circumferentially around the exterior of the pipe and, if extending around the entire circumference of the pipe, can provide a seal between the composite pipe and the inner surface of the tubular portion of the housing and the outer surface of the forge member. The number and arrangement of the ribs may be determined by the axial load capacity desired to be withstood by the composite pipe.
The composite pipe assembly may comprise an end fitting for the composite pipe, for example a flange, preferably mounted on the housing. Alternatively, the composite pipe assembly may act as a repair for a damaged section of the composite pipe or as a joint between two lengths of composite pipe.
In a further aspect, the present invention provides a method of applying an end fitting to a composite pipe, the composite pipe having a pipe wall having an inner surface and an outer surface, which method comprises: providing a housing having a tubular portion around the exterior of an end portion of the pipe wall; providing a tubular forge member within the pipe, whereby the end portion of the pipe wall extends between the forge member and the tubular portion of the housing; and deforming the forge member radially outwards, thereby deforming the tubular portion of the housing radially outwards beyond its partial yield point; whereby the tubular portion of the housing applies a radially inwards compressive force against the pipe wall and the forge member. Preferably, the forge member applies a force radially outwards against the inner surface of the pipe wall. The forge member is preferably deformed to beyond its yield point.
In one embodiment, the forge member is provided during the preparation of the composite pipe. In this embodiment, the layers of the end portion of the composite pipe are formed so as to overlie the outer surface of the forge member. While this embodiment precludes the installation of the assembly after the manufacture of the composite pipe, for example at a remote location in the field, it may result in a lower stress concentration in the composite material associated with the subsequent deforming of the forge member.
The tubular portion of the housing is preferably deformed such that it is partially yielded to no greater than 75%, more preferably to no greater than 50% of its yield point.
In still a further aspect of the present invention, there is provided a method of repairing a composite pipe comprising a pipe wall having an inner surface and an outer surface, the pipe wall having a damaged portion, which method comprises providing a housing having a tubular portion, the tubular portion of the housing extending around the exterior of the pipe wall covering the damaged region of the wall; providing a tubular forge member within the pipe such that the damaged region of the pipe wall is between the forge member and the tubular portion of the housing; and deforming the forge member radially outwards, thereby deforming the tubular portion of the housing radially outwards beyond its partial yield point; whereby the tubular portion of the housing applies a radially inwards compressive force against the pipe wall and the forge member. As before, the forge member once deformed preferably applies a force radially outwards against the inner surface of the pipe wall. Again, the forge member is preferably deformed to beyond its yield point.
The composite pipe may be formed with a metallic liner on its inside surface. Such a liner may be employed to seal the inside surface of the composite pipe to prevent leakage of fluid under pressure within the pipe. Such a composite pipe may be used in the methods and apparatus of the present invention as hereinbefore described. However, in a further embodiment the forge member may be formed as a unitary part with the metal liner. This may be achieved, for example, by forming the liner with an end portion of increased thickness.
A further aspect of the invention provides a fitting assembly for a composite pipe having a pipe wall with an inner surface and an outer surface, the fitting assembly comprising a housing having a tubular portion having an inner surface, which tubular portion is sized to extend around the exterior of a portion of the pipe wall; a tubular forge member having an outer surface for location within the composite pipe, whereby a portion of the of the pipe wall is between the outer surface of the tubular forge member and the inner surface of the tubular portion of the housing; the tubular forge member being deformable in a radially outward direction to thereby deform the tubular portion of the housing beyond its partial yield point, such that the tubular portion of the housing applies a residual compressive force radially inwards against the pipe wall and the forge member. The forge member is preferably formed so as to be deformable such that it will apply a force radially outwards against the inner surface of the pipe wall.